Seeing as you here it inside with the windows up better I am going to assume this is alternator whine. Do you by any chance have an aftermarket cd player/amplifier setup. Poor grounding of these components can lead to feedback in your speaker wires resulting in a buzzing or whining sound that attenuates from the speakers. If it does have an aftermarket audio system check your ground behind your head unit. I find that if you use the stock ground in the harness this can occur quite often.